1. Technical Field
The invention relates to the printing of images, which exist in a digital electronic format. More particularly, the invention relates to a printing method and apparatus having multiple raster image processors.
2. Description of the Prior Art
Every image that exists in a digital electronic format is made of picture elements. At some point, all such digital image data, whether expressed as vector format data or bitmap format data, must be rendered into pixels for display on a monitor or for printing on a printer. All images, therefore, have pixels as their base. Rendering, or translating the digital data into physical output, is the most important part of realizing such images. The term raster image processing (RIP) refers to the process of translating digital image data into physical visual images and graphics. FIG. 1 is a block schematic diagram showing a conventional raster imaging processor in which raster images are images composed of lines of pixels. In raster image processing, each horizontal line of bitmap image pixel information is referred to as a scan line or raster line. In FIG. 1, Postscript.RTM. lines and/or digital RGB or CMYK pixels 12 are shown processed by associated RIPs 13-15 to produce information that results in a physical output 16.
The simplest output devices translate only one raster line at a time and then output that line to film, paper, or a monitor. FIG. 2 is an illustration of an image 20 and a single raster line 22 as processed by such device. More efficient RIP techniques analyze an image all at one time and convert the image information into visual output.
The RIP is a program that may be embedded in hardware or the may exist entirely in software. A hardware RIP is a computer which is attached to an output device and which is dedicated to translating digital image data for output. Image data is sent from a workstation to a computer that is attached to the output device. The hardware RIP program which resides in this computer interprets the image data and provides raw on/off instructions to the output device. The actual interpreter may be any program that translates image information in accordance with a known format. For example, the Postscript.RTM. interpreter manufactured by Adobe Corporation of Mountain View, Calif. is commonly used in raster image processing.
A software RIP performs many of the same functions as a hardware RIP. The software RIP is usually located at a workstation that is not necessarily dedicated solely to the RIP function. The software RIP interprets the digital image data and produces therefrom information that is required for the output device to function properly. A major disadvantage of software RIPs is that the workstation may not be configured to perform at speeds equal to a dedicated hardware RIP. Software RIPs are also presently less desirable for larger print facilities because such RIPs usually require a large amount of free hard disk space on the workstation. Such hard disk storage is necessary because all of the digital data that are processed must be saved before they are sent to the output device.
The RIPing process is complex and much of the output device rating is based upon the device's image processing speed. The speed of the interpreter or RIP is a major factor in the efficiency of the entire image reproduction process. Because of the dedicated computer, hardware RIPs are typically faster than software RIPs. Even so, it would be advantageous to provide improvements in RIP architectures that increase processing speed and efficiency.